The present invention relates to an improved fluid scroll machine such as a scroll vacuum pump.
FIG. 6 is a sectional view of a conventional fluid scroll machine comprising a casing 1 in which lubricating oil 10 is accumulated at the bottom of the casing, an electric motor 2 provided in the casing and having a rotary shaft 3 supported by a bearing support 4 and a shelf 5, a fixed scroll 6 coupled to the shelf, a movable scroll 7 which is eccentrically rotated relative to the fixed scroll by the rotary shaft, an air feed port 8 communicating with the interior of the fixed scroll, and an air discharge port 9 through which air compressed by the fixed and the movable scrolls is discharged. In the fluid scroll machine, a balancing ring 11 is attached to the rotary shaft 3 to prevent rotative imbalance at the time of the rotation of the movable scroll 7 to keep the machine from undergoing a large vibration. If the machine is small in size, the balancing ring 11 can be made relatively small in size. However, if the machine is middle or large in size, the balancing ring 11 needs to be made middle or large in size. In the latter case, the outside diameter and length of the balancing ring 11 need to be made so large that the cost thereof is high. This is a problem.
In addition, since the rigidity of the engaged portion 7b of the movable scroll 7 decreases toward the outer end 7c of the portion, the portion is deflected at the outer end thereof outward in the radial direction of the scroll by the pushing force of the end mill machining of the inside portion, as shown by a dotted line in FIG. 7. After the machining is completed, the engaged portion 7b returns from the deflected position thereof to the original position thereof due to the elasticity thereof. For that reason, the dimensional accuracy of the finished movable scroll cannot be made high. This is another problem.